Dr Christopher Bridges

Biography

Dr Chris Bridges obtained a BEng in Electronics at the University of Greenwich and was previously employed at BAE Systems in Rochester, Kent. He joined Surrey Space Centre as a PhD student in April 2006 under Dr Tanya Vladimirova and has since been successful in obtaining Post Doctorial positions in the VLSI Design & Embedded Systems and Astrodynamics Groups. He is now the On-Board Data Handling Group lead and is published in agent computing, Java processing, and multi-core system-on-a-chip technologies. He runs the Implementing Intelligence for Aerospace Session at the IEEE/AIAA Aerospace Conference at Big Sky, Montana, USA.

Chris is the Surrey Space Centre (SSC) Lead Engineer & Researcher for the collaboration with Surrey Satellite Technology Ltd (SSTL) mission 'Surrey Training Research and Nanosatellite Demonstrator' programme (STRaND). STRaND-1 began in April 2010 and aims to fly the latest smartphone technologies and advanced attitude orbit and control system (AOCS). STRaND-2 aims to fly two nanosatellites towards close-proximity operations/imaging and rendezvous & docking demonstration utilising the Microsoft Kinect.

Chris is passionate about communicating all things space through his teaching, regular media, and social websites. Read more about Chris on his UK Space Agency Career Profile page. Keep up to date on current events & news on the Surrey Space Centre Facebook or SpaceAtSurrey Twitter!

Research Collaborations

Visual Inspection Payload - Astrodynamics Group

The feasibility of performing a visual inspection mission between two satellites is being investigated utilising a microelectromechanical (MEMS) thruster built by EADS Astrium. The combined thrusting, imaging, and processing requirements will go towards a new integrated hardware and software payload design.

AMSAT-UK and ESA - ESEO Mission

The OBDH Group has been bring together technologies for a VHF and L-band communication system where Dr Bridges' group and students have been working on automotive components and software defined radio technologies to fly a new radio architecture.

Abstract

The European Student Earth
Orbiter (ESEO) is a micro-satellite mission
to low Earth orbit and is being developed,
integrated, and tested by European
university students as an ESA Education
Office project. AMSAT-UK and Surrey
Space Centre are contributing to the mission
with a transceiver and transponder similar
to that of FUNcube-1 with the addition
of utilising a Atmel AT32 processor for
packet software-redundancy, baseband
processing, forward error correction, and
packet forming; acting as a step towards
software defined radio using low MIPS
automotive microprocessors. As on the
FUNcube-1 satellite, the telemetry formats
and encoding schemes presented utilize a
large ground network of receivers on the
VHF downlink and conforms to 1200 bps
and a new 4800 bps redundant downlink
for the rest of the spacecraft. The uplink is
on L-band using bespoke partial-CCSDS
frames.

Abstract

The ongoing evolution in constellation/formation of CubeSats along with steadily increasing number of satellites deployed in Lower Earth Orbit (LEO), demands a generic reconfigurable multimode communication platforms. As the number of satellites increase, the existing protocols combined with the trend to build one control station per CubeSat become a bottle neck for existing communication methods to support data volumes from these spacecraft at any given time. This paper explores the Software Defined Radio (SDR) architecture for the purposes of supporting multiple-signals from multiple-satellites, deploying mobile and/or distributed ground station nodes to increase the access time of the spacecraft and enabling a future SDR for Distributed Satellite Systems (DSS). Performance results of differing software transceiver blocks and the decoding success rates are analysed for varied symbol rates over different cores to inform on bottlenecks for Field Programmable Gate Array (FPGA) acceleration. Further, an embedded system architecture is proposed based on these results favouring the ground station which supports the transition from single satellite communication to multi-satellite communications.

Abstract

The AlSat-Nano mission is a joint endeavour by the UK and Algeria to build and operate a 3U CubeSat. The project was designed to provide training to Algerian students, making use of UK engineering and experience. The CubeSat was designed and built by the Surrey Space Centre (SSC) of the University of Surrey and hosts three UK payloads with operations run by the Algerian Space Agency (ASAL). The educational and CubeSat development were funded by the UK Space Agency (UKSA), whilst the UK payloads were self-funded. Launch and operations are funded by ASAL. This paper illustrates the development of the programme, the engineering of the satellite and the development of collaborative operations between the SSC and ASAL.

Abstract

Proximity flight systems for rendezvous-and-docking, are traditionally the domain of large, costly institutional
manned missions, which require extremely robust and expensive Guidance Navigation and Control (GNC) solutions.
By developing a low-cost and safety compliant GNC architecture and design methodology, low cost GNC solutions
needed for future missions with proximity flight phases will have reduced development risk, and more rapid
development schedules. This will enable a plethora of on-orbit services to be realised using low cost satellite
technologies, and lower the cost of the services to a point where they can be offered to commercial as well as
institutional entities and thereby dramatically grow the market for on-orbit construction, in-orbit servicing and active
debris removal. It will enable organisations such as SSTL to compete in an area previously exclusive to large
institutional players. The AAReST mission (to be launched in 2018), will demonstrate some key aspects of low cost
close proximity “co-operative” rendezvous and docking (along with reconfiguration/control of multiple mirror
elements) for future modular telescopes. However this is only a very small scale academic mission demonstration
using cubesat technology, and is limited to very close range demonstrations.
This UK National Space Technology Programme (NSTP-2) project, which is being carried out by SSTL and SSC, is
due to be completed by the end of November 2017 and is co-funded by the UK Space Agency and company R&D. It
is aiming to build on the AAReST ("Autonomous Assembly of a Reconfigurable Space Telescope") mission (where
appropriate), and industrialise existing research, which will culminate in a representative model that can be used to
develop low-cost GNC solutions for many different mission applications that involve proximity activities, such as
formation flying, and rendezvous and docking. The main objectives and scope of this project are the following:
 Definition of a reference mission design (based on a scenario that SSTL considers credible as a realistic
scenario) and mission/system GNC requirements.
 Develop a GNC architectural design for low cost missions applications that involve close proximity
formation flying, rendezvous and docking (RDV&D) - i.e. “proximity activities”
 Develop a low cost sensor suite suitable for use on proximity missions
 Consider possible regulatory constraints that may apply to the mission
The SSTL/SSC reference mission concept is a

Abstract

The European Student Earth Orbiter (ESEO) is a micro-satellite mission to Low Earth Orbit and is being developed, integrated, and tested by European university students as an ESA Education Office project. AMSAT-UK and Surrey Space Centre are contributing to the mission with a transceiver and transponder similar to that of FUNcube-1 with the addition of utilising a Atmel AT32 processor for packet software-redundancy, baseband processing, forward error correction, and packet forming; acting as a step towards software defined radio using low MIPS automotive microprocessors. As on the FUNcube-1 satellite, the telemetry formats and encoding schemes presented utilize a large ground network of receivers on the VHF downlink and conforms to 1200 bps and a new 4800 bps redundant downlink for the rest of the spacecraft. The uplink is on L-band using bespoke partial-CCSDS frames. This paper details the flight software on the engineering and flight models to ESA, and the technical configuration and associated tests of demonstrating the processor load is under for varying operating and sampling modes. In particular, a key contribution will be the details of utilising the Google Test Suite for verification of the SDR functions and FreeRTOS tools to optimize processor load margins to 30% when operating parallelized ADC and DAC, and CAN-open telemetry chains and what memory considerations are needed to ensure stable long-term operations.

Abstract

The current trend in commercial processors is producing multi-core architectures which pose both an opportunity and a challenge for future space based processing. The opportunity is how to leverage multi-core processors for high intensity computing applications and thus provide an order of magnitude increase in onboard processing capability with less size, mass, and power. The challenge is to provide the requisite safety and reliability in an extremely challenging radiation environment. The objective is to advance from multiple single processor systems typically flown to a fault tolerant multi-core system. Software based methods for multi-core processor fault tolerance to single event effects (SEEs) causing interrupts or ‘bit-flips’ are investigated and we propose to utilize additional cores and memory resources together with newly developed software protection techniques. This work also assesses the optimal trade space between reliability and performance. Our work is based on the modern compiler “LLVM” as it is ported to many architectures, where we implement optimization passes that enable automatic addition of protection techniques including Nmodular redundancy (NMR) and error detection and correction (EDAC) at assembly/instruction level to languages supported. The optimization passes modify the intermediate representation of the source code meaning it could be applied for any high level language, and any processor architecture supported by the LLVM framework. In our initial experiments, we implement separately triple modular redundancy (TMR) and error detection and correction codes including (Hamming, BCH) at instruction level. We combine these two methods for critical applications, where we first TMR our instructions, and then use EDAC as a further measure, when TMR is not able to correct the errors originating from the SEE. Our initial experiments show good performance (about 10% overhead) when protecting the memory of code using double error detection single error correction hamming code and TMR (Triple modular redundancy), further work is needed to improve the performance when protecting the memory of code using the BCH code. This work would be highly valuable, both to satellites/space but also in general computing such as in in aircraft, automotive, server farms, and medical equipment (or anywhere that needs safety critical performance) as hardware gets smaller and more susceptible.

Abstract

Continual advancements in Earth Observation (EO) optical imager payloads has led to a significant increase in the volume of multispectral data generated onboard EO satellites. As a result, a growing onboard data bottleneck need to be alleviated. One technique commonly used is onboard image compression. However, the performance of traditional space qualified processors, such as radiation hardened FPGAs, are not able to meet current nor future onboard data processing requirements. Therefore, a new high capability hardware architecture is required. In previous work a new GPU accelerated scalable heterogeneous hardware architecture for onboard data processing was proposed. In this paper, two new CUDA GPU implementations of the state-of-the-art lossless multidimensional image compression algorithm CCSDS-123, are discussed. The first implementation is a generic CUDA implementation of the CCSDS-123 algorithm whilst the second is optimised specifically for multispectral EO imagery. Both implementations utilise image tiling to leverage an additional axis for algorithm parallelisation to increase processing throughput. The CUDA implementation and optimisation techniques deployed are discussed in the paper. In addition, compression ratio and throughput performance results are presented for each implementation. Further experimental studies into the relationships between algorithm user definable compression parameters, tile sizes, tile dimensions and the achieved compression ratio and throughput, were performed.

Abstract

While small, low-cost satellites continue to increase in capability and popularity, their reliability remains a problem. Traditional techniques for increasing system reliability are well known to satellite developers, however, their implementation on low-cost satellites is often limited due to intrinsic mass, volume and budgetary restrictions. Aiming for graceful degeneration, therefore, may be a more promising route. To this end, a stem-cell-inspired, multicellular architecture is being developed using commercial-off-the-shelf components. It aims to replace a significant portion of a typical satellite’s bus avionics with a set of initially identical cells. Analogous to biological cells, the artificial cells are able to differentiate during runtime to take on a variety of tasks thanks to a set of artificial proteins. Each cell reconfigures its own proteins within the context of a system-wide distributed task management strategy. In this way, essential tasks can be maintained, even as system cells fail. This paper focusses on two hardware implementations of the stem-cell inspired architecture. The first implementation, based on a single cell, serves as the Payload Interface Computer on a CubeSat named SME-SAT. The second hardware implementation is a benchtop system composed of several cells intended to demonstrate a complete multicellular system in operation. In order to demonstrate the feasibility of these multicellular architectures, the physical attributes of the hardware implementations are compared to those of more traditional implementations and are shown to have enhanced reliability at the cost of increased power and internal bus bandwidth.

Abstract

Flight and ground segment software in university missions is often developed only after hardware has matured sufficiently towards flight configuration and also as bespoke codebases to address key subsystems in power, communications, attitude, and payload control with little commonality. This bespoke software process is often hardware specific, highly sequential, and costly in staff/monitory resources and, ultimately, development time. Within Surrey Space Centre (SSC), there are a number of satellite missions under development with similar delivery timelines that have overlapping requirements for the common tasks and additional payload handling. To address the needs of multiple missions with limited staff resources in a given delivery schedule, computing commonality for both flight and ground segment software is exploited by implementing a common set of flight tasks (or modules) which can be automatically generated into ground segment databases to deliver advanced debugging support during system end-to-end test (SEET) and operations.
This paper focuses on the development, implementation, and testing of SSC’s common software framework on the Stellenbosch ADCS stack and OBC emulators for numerous missions including Alsat-1N, RemoveDebris, SME-SAT, and InflateSail. The framework uses a combination of open-source embedded and enterprise tools such as the FreeRTOS operating system coupled with rapid development templates used to auto-generate C and Python scripts offline from ‘message databases’. In the flight software, a ‘core’ packet router thread forwards messages between threads for inter process communication (IPC). On the ground, this is complemented with an auto-generated PostgreSQL database and web interface to test, log, and display results in the SSC satellite operations centre. Profiling is performed using FreeRTOS primitives to manage module behaviour, context, time and memory – especially important during integration. This new framework has allowed for flight and ground software to be developed in parallel across SSC’s current and future missions more efficiently, with fewer propagated errors, and increased consistency between the flight software, ground station and project documentation.

Abstract

Low-cost satellites continue to grow in popularity
and capability, but have shown poor on-orbit performance to
date. While traditional satellite missions have relied upon expensive
fault prevention techniques, such as component screening, the
use of radiation hardened components, and extensive test campaigns,
low-cost missions must focus on fault tolerance, instead.
This paper describes a novel, fault-tolerant system architecture,
named Satellite Stem Cells. The Satellite Stem Cell Architecture,
which is based on artificial cells, evolved from research into
traditional reliability theory, bio-inspired engineering, and agentbased
computing. Traditional reliability theory points towards
k-out-of-n architectures for their superior reliability, while cell
biology demonstrates how to build extremely multifunctional
subsystems. Finally, agent computing provides a solution for
facilitating the cooperation of a set of autonomous cells in a
peer-to-peer environment. This paper describes the development
of the architecture, details the artificial cell design, and gives
preliminary implementation details

Abstract

Future space telescopes with diameter over 20 m will require in-space assembly. High-precision formation flying has very high cost and may not be able to maintain stable alignment over long periods of time. We believe autonomous assembly is a key enabler for a lower cost approach to large space telescopes. To gain experience, and to provide risk reduction, we propose a demonstration mission to demonstrate all key aspects of autonomous assembly and reconfiguration of a space telescope based on multiple mirror elements. The mission will involve two 3U CubeSat-like nanosatellites (“MirrorSats”) each carrying an electrically actuated adaptive mirror, and each capable of autonomous un-docking and re-docking with a small central “9U” class nanosatellite core, which houses two fixed mirrors and a boom-deployed focal plane assembly. All three spacecraft will be launched as a single ~40kg microsatellite package.

Abstract

Modern computers are now far in advance of satellite systems and leveraging of these technologies for space applications could lead to cheaper and more capable spacecraft. Together with NASA AMES’s PhoneSat, the STRaND-1 nanosatellite team has been developing and designing new ways to include smart-phone technologies to the popular CubeSat platform whilst mitigating numerous risks. Surrey Space Centre (SSC) and Surrey Satellite Technology Ltd. (SSTL) have led in qualifying state-of-the-art COTS technologies and capabilities - contributing to numerous low cost satellite missions. The focus of this paper is to answer if 1) modern smart-phone software is compatible for fast and low cost development as required by CubeSats, and 2) if the components utilised are robust to the space environment. The STRaND-1 smart-phone payload software explored in this paper is united using various open-source Linux tools and generic interfaces found in terrestrial systems. A major result from our developments is that many existing software and hardware processes are more than sufficient to provide autonomous and operational payload object-to-object and filebased management solutions. The paper will provide methodologies on the software chains and tools used for the STRaND-1 smartphone computing platform, the hardware built with space qualification results (thermal, thermal vacuum, and TID radiation), and how they can be implemented in future missions.

Abstract

STRaND-1 is the first in a series of Surrey Satellite Technology Ltd. (SSTL)-Surrey Space Centre (SSC)
collaborative satellites designed for the purpose of technology path finding for future commercial operations. It is the
first time Surrey has entered the CubeSat field and differs from most CubeSats in that it will fly a modern
Commercial Off The Shelf (COTS) Android smartphone as a payload, along with a suite of advanced technologies
developed by the University of Surrey, and a payload from the University of Stellenbosch in South Africa. STRaND-
1 is also different in that anyone (not just from the space engineering or space science community) will be eligible to
fly their “app" in space, for free. STRaND-1 is currently being manufactured and tested by volunteers in their own
free time, and will be ready for an intended launch in the first quarter of 2012.
This paper outlines the STRaND pathfinder programme philosophy which challenges some conventional space
engineering practises, and describes the impact of those changes on the satellite development lifecycle. The paper
then briefly describes the intent behind the design of STRaND-1, before presenting details on the design of the
nanosatellite, focussing of the details of the innovative new technologies. These technologies include two different
propulsion systems, an 802.11g WiFi experiment, a new VHF/UHF transceiver unit and a miniature 3-axis reaction
wheel assembly. The novel processing setup (which includes the smartphone) is discussed in some detail,
particularly the potential for outreach via the open source nature of Google's Android operating system. A stepthrough
of the planned concept of operations is provided, which includes a possible rendezvous and inspection
objective, demonstrating equal or improved capability compared to SNAP-1 with a reduced total system mass.
Finally, data from the test campaign is presented and compared against other notable CubeSats known for their
advanced capabilities. Rendered images of STRaND-1 are shown in Fig. I and are discussed later in the paper.

Abstract

Satellite constellation deployment for formation flying missions is one of the key areas for consideration when realizing the final constellation with reduced propellant mass requirements on the propulsion system. The use of a single launch vehicle to deploy multiple satellites into a formation is faster and cheaper but there is greater risk of collision. This risk must be managed with the competing desire to establish a relatively tight formation for better inter-satellite communication. The launcher attitude, satellite injection times and velocities are key parameters to safely achieve a given separation distance and distribution. This paper presents a visual simulator to propagate the satellite trajectories from the launcher using an expanded definition of Hill's equations, and extending to polar relative motion. It is assumed that a simple launcher is used which is incapable of reposition once in orbit. Low injection velocities are exploited to inject large numbers satellites into a stable constellation. Utilizing small tight natural motion formations help to reduce perturbations and the propellant mass required for formation maintenance. SatLauncher is a new visualization tool for investigating the relative motion and key parameters between satellites in these new missions and applications for multi-satellite launchers without the need for any further industrial tool. The QB50 mission is taken forward as a representative scenario requiring our latest software tool and new methods are presented towards collision free formation deployment.

Abstract

Distributed satellite systems are large research topics, spanning many fields such as communications, networking schemes, high performance computing, and distributed operations. DARPA's F6 fractionated spacecraft mission is a prime example, culminating in the launch of technology demonstration satellites for autonomous and rapidly configurable satellite architectures. Recent developments at Surrey Space Centre have included the development of a Java enabled system-on-a-chip solution towards running homogenous agents and middleware software configurations.